1. Field of the Invention
This invention relates to gas turbines, and in particular relates to turbine blades such as moving blades and stationary blades equipped in gas turbines.
2. Description of the Related Art
FIG. 4 shows a cross section of an approximately center portion of a stationary blade of a second row (row 2) (hereinafter, referred to as a turbine blade) equipped in a turbine unit (not shown) along with the plane substantially perpendicular to an axial line in a vertical or upright direction.
That is, a typical example of a turbine blade 10 shown in FIG. 4 comprises a turbine blade body 20 and inserts 30.
In the plane substantially perpendicular to an axial line of the turbine blade body 20 in the vertical direction, a leading edge xe2x80x98L.E.xe2x80x99 is connected with a trailing edge xe2x80x98T.E.xe2x80x99 by a xe2x80x98curvedxe2x80x99 center line xe2x80x98C.L.xe2x80x99. A sheet of a plate-like rib 22 is arranged substantially perpendicular to the center line C.L. and partitions the interior space of the turbine blade 20 into two cavities C1 and C2. Air holes 24 having pin fins 23 are arranged with respect to the cavity C2 that is arranged in the side of the trailing edge T.E., wherein they force the cooling air in the cavity C2 to flow towards the exterior of the turbine blade body 20.
The insert 30 has a hollow shape and provides the prescribed number of impingement cooling holes 31. One insert 30 is inserted into each of the cavities C1 and C2 in such a way that a cooling space C.S. is formed between an exterior surface 32 of the insert 30 and an interior surface 25 of the turbine blade body 20.
In the turbine blade 10 having the aforementioned structure, the cooling air is introduced into the internal spaces of the inserts 30 by a specific means (not shown); then, the cooling air is forced to flow into the cooling spaces C.S. through the impingement holes 31 as shown by solid arrows in FIG. 5, so that the turbine blade body 20 is subjected to impingement cooling. Then, the cooling air is further forced to flow outwards through plural film cooling holes 21 arranged in exterior walls of the turbine blade body 20. This causes film layers formed around exterior walls of the turbine blade body 20 due to the cooling air, so that the turbine blade body 20 is subjected to film cooling. In addition, the cooling air spurts out through the air holes 24 from the trailing edge T.E. Herein, the proximal portion of the trailing edge T.E. of the turbine blade body 20 is cooled down by the cooling air cooling the pin fins 23.
In the aforementioned turbine blade 10, however, the cooling efficiency may be deteriorated with respect to the pin fins 23 that are arranged in proximity to the trailing edge T.E. of the turbine blade body 20. This causes a problem in that in order to cool down the pin fins 23, a considerable amount of cooling air should be forced to spurt out from the impingement cooling holes 31 of the insert 30 that is arranged in the cavity C2.
Since a considerable amount of cooling air is forced to spurt out from the impingement cooling holes 31 of the insert 30 arranged in the cavity C2, the corresponding portion, that is, the center portion of the turbine blade body 20 shown in FIGS. 4 and 5 must become excessively cool compared with other portions such as the leading edge portion locating the cavity C1 and the trailing edge portion locating the pin fins 23 and air holes 24. This causes a problem in that unwanted temperature differences occur within the turbine blade body 20.
In addition, there is a problem in that when temperature differences occur within the turbine blade body 20, thermal stress must occur due to differences of thermal expansions.
It is an object of the invention to provide a turbine blade that can reduce the amount of cooling air and improve the overall performance of a gas turbine using it.
It is another object of the invention to provide a turbine blade that can reduce temperature differences within a turbine blade body to be as low as possible.
A turbine blade applicable to a gas turbine has a turbine blade body having film cooling holes, the interior space of which is partitioned into two cavities by a rib having a plate-like shape. The rib is arranged substantially perpendicular to the center line connecting between the leading edge and trailing edge in the plane substantially perpendicular to the axial line of the turbine blade body in the vertical direction. Inserts are respectively arranged in the cavities in such a way that the cooling space is formed between the exterior surface of the insert and the interior surface of the turbine blade body. The inserts each have a hollow shape and impingement holes. In addition, a communication means such as bypass holes and slit(s) is formed with the rib to provide a communication between the cavity arranged in the leading-edge side and the cavity arranged in the trailing-edge side in the turbine blade body.
In the above, the cooling air that is introduced into the inserts is forced to flow into the cooling spaces via the impingement holes. Thus, the turbine blade body is subjected to impingement cooling. Then, the cooling air spurts out from the film cooling holes, thus forming film layers around the turbine blade body. Thus, the turbine blade body is subjected to film cooling. Herein, a part of the cooling air in the cooling space arranged in the leading-edge side is guided and is forced to flow into the cooling space arranged in the trailing-edge side. Therefore, it contributes to the cooling of the cooling space arranged in the trailing-edge side. Specifically, the cooling air transmitted through the communication means formed with the rib is transmitting through and is cooling the cooling space arranged in the trailing-edge side; then, it is forced to flow out from the trailing edge of the turbine blade body while cooling pin fins.
The communication means is arranged in either the rear side or front side, which has a good heat transmission in the turbine blade body. That is, the impingement cooling is interrupted with respect to the prescribed side having a good heat transmission compared with the other side in the turbine blade body.
Further, a partition wall can be arranged between the rib and the insert arranged in the trailing-edge side, thus providing a separation between the cooling space arranged in the rear side and the cooling space arranged in the front side in the turbine blade body. That is, it is possible to prevent the cooling air transmitted through the communication means from proceeding to the cooling space of the front side (or rear side) from the cooling space of the rear side (or front side). In other words, it is possible to prevent the impingement cooling of the front side (or rear side) from being interrupted by the cooling space that is transmitted through the communication means from the rear side (or front side) in the turbine blade body.
Thus, it is possible to noticeably reduce the amount of cooling air transmitted within the turbine blade body. In addition, it is possible to reduce temperature differences entirely over the turbine blade body as small as possible. That is, it is possible to reliably improve the performance entirely over the gas turbine using the aforementioned turbine blade.